There are four G-protein-coupled receptors (GPCRs) which interact with the ligand prostaglandin E2 which are designated subtypes EP1, EP2, EP3 and EP4. The EP1 receptor is a 7-transmembrane receptor and its natural ligand is the prostaglandin PGE2. PGE2 also has affinity for the other EP receptors (types EP2, EP3 and EP4). The EP1 receptor is associated with smooth muscle contraction, pain (in particular inflammatory, neuropathic and visceral), inflammation, allergic activities, renal regulation and gastric or enteric mucus secretion.
Prostaglandin E2 (PGE2) exerts pain and pain related entities such as allodynia and hyperalgesia through the EP1, EP4 and EP3 receptor subtypes (Woodward et al. Pharmacol Rev. 63: 471-538, 2011). Furthermore, it has been shown that in the EP1 knockout mouse pain-sensitivity responses are reduced by approximately 50%. EP1 receptor antagonist (ONO-8711) reduces hyperalgesia and allodynia in a rat model of chronic constriction injury and inhibits mechanical hyperalgesia in a rodent model of post-operative pain. The efficacy of EP1 receptor antagonists in the treatment of visceral pain in a human model of hypersensitivity has been demonstrated. Thus, selective prostaglandin ligands depending on which prostaglandin EP receptor subtype is being considered, have anti-inflammatory, antipyretic and analgesic properties similar to a conventional non-steroidal anti-inflammatory drug, and in addition, inhibit hormone-induced uterine contractions and have anti-cancer effects. These compounds have a diminished ability to induce some of the mechanism-based side effects of NSAIDs which are indiscriminate cyclooxygenase inhibitors. In particular, the compounds have a reduced potential for gastrointestinal toxicity, a reduced potential for renal side effects, a reduced or absent potential for cardiovascular risk, a reduced effect on bleeding times and a lessened ability to induce asthma attacks in aspirin-sensitive asthmatic subjects. Moreover, as a result of sparing potentially beneficial prostaglandin pathways, these agents may have enhanced efficacy over NSAIDS and/or COX-2 inhibitors. (See Pub. No. US 2005/0065200, which is hereby incorporated by reference in its entirety, for other diseases that may be treated by EP4 receptor antagonists).
The TP (also known as TxA2) receptor is a prostanoid receptor subtype stimulated by the endogenous mediator thromboxane. Activation of this receptor results in various physiological actions primarily incurred by its platelet aggregatory and smooth muscle constricting effects, thus opposing those of prostacyclin receptor activation.
TP receptors have been identified in human kidneys in the glomerulus and extraglomerular vascular tissue. Activation of TP receptors constricts glomerular capillaries and suppresses glomerular filtration rates indicating that TP receptor antagonists could be useful for renal dysfunction in glomerulonephritis, diabetes mellitus and sepsis.
Activation of TP receptors induces bronchoconstriction, an increase in microvascular permeability, formation of mucosal edema and mucus secretion, which are typical characteristic features of bronchial asthma. TP antagonists have been investigated as potential asthma treatments resulting in, for example, orally active Seratrodast (AA-2414). Ramatroban is another TP receptor antagonist currently undergoing phase III clinical trials as an anti-asthmatic compound.
Since the DP1 receptor may trigger an asthmatic response in certain individuals, compounds that have DP1 antagonist properties may be useful as anti-asthmatic drugs. (See Pub. No. 2004/0162323, which is hereby incorporated by reference in its entirety, for the disclosure of other diseases and conditions that may be treated with DP antagonists.)
Finally, the FP receptor modulates intraocular pressure and mediates smooth muscle contraction of the sphincter muscles in the gastrointestinal tract and the uterus and contractile smooth muscle of these and other organs. Thus, antagonists of the FP receptor are useful for treating reproductive disorders. (See U.S. Pat. No. 6,511,999 which is hereby incorporated by reference in its entirety, for other diseases and conditions that may be treated with FP receptor antagonists.)
As further background for the present invention, see US Published Patent Application 2007/0060596, U.S. Pat. No. 8,494,424 and U.S. application Ser. No. 13/746,023, all of which are hereby incorporated by reference in their entireties.